This invention relates generally to the monitoring, servicing, and maintaining of electric circuits comprising connections made with wires and more specifically to a system for tracing electric circuits using a transmitter and a receiver.
Circuit tracers are typically used to locate the wires of electric circuits when the wires are not easily accessible. Such uses include identifying circuit breakers, fuses, blown fuses, junction boxes, shorts to ground, and breaks in wires, to name a few. The electric circuits with which circuit tracers are used usually comprise insulated wires joining one connection point to another connection point over some distance. A connection point may be, for example, a junction box, switch, power outlet, circuit breaker, fuse, or other such connection point, to name a few. During operation of the circuit tracer, the transmitter is turned on and electrically coupled to a connection point of the electric circuit. For example, to determine which circuit breaker is associated with a particular outlet, the transmitter is connected to the power outlet in question. This may be done by connecting probes directly to the outlet and then turning on the transmitter to input a signal on the electric circuit. The user then utilizes the receiver to search for the signal at the circuit breaker location. The receiver indicates reception and strength of the transmitted signal in some manner, and then by indicating the strength of the received signal, the user can determine the precise location of the circuit by finding the location with the strongest signal. This is useful in construction situations where the wires connecting the circuit breaker and power outlet are inaccessible.
A circuit tracer typically includes a transmitter and a receiver. The transmitter may include a power supply such as a battery, a circuit for generating a signal to be detected, and connector for applying said signal on to the electric circuit.
Two common methods exist to couple the transmitter to the electric circuit. First, a direct physical connection can be made to the electrical circuit such as through the use of conductive clips, leads, probes, or other such devices. Second, an indirect connection can be made by inductively coupling a signal to the electrical circuit. This method is preferable when the wire connecting the electric circuit is insulated and no direct electrical connection can be achieved without damaging the insulation. Inductive transmission operates by using the principles of electromagnetic mutual inductance, which state that any change of magnetic flux (current) in one conductor will induce a voltage in another conductor. Thus, this principle is used to impose a signal onto a wire by subjecting the wire to a magnetic field set up by an alternating current (AC) signal transmitter circuit. Typically, the AC circuit in the transmitter is connected to ferrous material in the shape of a generally circular clamp. The spring-loaded clamp opens so that it may be placed in a position where it surrounds the wire. As the signal transmitter circuit outputs the signal to the clamp connected to it, a like signal is induced on the wire, which is surrounded by the clamp.
Various types of configurations exist for the transmitter units with inductive clamps. For example, the inductive clamp unit may be permanently fixed to the transmitter. Alternatively, the clamp unit may be connected to the transmitter through a cable. Some transmitters may also include provisions for direct connections in addition to an inductive method using a clamp. Further, power for both the clamp and transmitter may be supplied in any number of ways such as internal battery power or external battery power.
The receiver also exists in a variety of configurations. The antenna or detection portion of the receiver unit may be permanently fixed to the receiver, or it may be connected remotely through a cable. The means of communicating with the user may utilize any number of technologies, alone or in combination with one another. For example, the receiver may incorporate an audio alert indicating to the user that the electric circuit has been detected. Alternatively, the receiver may use a visual display to indicate a certain response to the transmitter signal. Furthermore, a receiver may use a combination of methods to communicate to the user. As with the transmitter, the receiver may be powered any number of ways including external sources or internal batteries to name a few.
Because the signal strength measurement is an important element of the circuit tracer in determining the location of the circuit, detection circuitry is critical. Complicating the detection method is the fact that the receiver needs to be sensitive enough to be able to detect the low power signal over a wide area yet not overload the receiver with a strong signal when in close proximity to the wire being traced.
Another difficulty with typical receivers is the visual display. During use of the receiver, a user may typically hold the receiver unit with the display at a variety of different orientations while tracing wires. The problem with the display is that at some orientations of the receiver, such as 180 degrees from normal, it becomes difficult to read. Depending on the location of the wires being traced, the user may not be able to hold the unit at an acceptable orientation due to physical limitations, so the display becomes difficult to read.
Physical location may also a problem for the transmitter unit. In small physical locations where a minimum of space exists and the inductive clamp is needed, the transmitter unit can become cumbersome. Because the clamp must be connected either as part of the unit or through a cable, it uses up valuable space or otherwise hinders the user from placing the transmitter at the needed location.
Since circuit tracers are often used to identify a circuit breaker needed to disconnect power from a circuit, the transmitter is often connected to power outlet terminals. However, after a circuit breaker has been opened to remove power on the circuit, the conventional circuit tracer receiver provides no indication to the user if power has indeed been disconnected on the desired circuit. For a variety of reasons, the wrong circuit breaker is sometimes opened, and users assume they have opened the correct one without verifying if there is power on the circuit. Thus, a safety hazard may be created through the use of circuit tracers because they do not confirm that power has been removed from a selected circuit.